IMO the idea of an open PvE proposal is impractical, I gave some reasoning on why I think so in an
earlier post.
Mobius and other PvE private groups don't disable PvP either, the potential to be harrassed by other players is present in all multiplayer modes with the only deterrent being a potential ban after the fact that's open to abuse. I gave up my slot in the Mobius private group for someone else to use years ago (shortly before the regional groups were created) but I do remember being scanned by another Mobius player while docked & failing missions that I had only just taken because of it. They apologised & professed ignorance when I told them what happened but of course the act was still able to be done.
My ironic comment about Legacy was more about how quiet it is; you are correct that nothing has changed wrt Open PvE (for completeness there have been no moves in the direction of an Open Only or client/server networking model either and there are now even more ways to fail to instance with another player than before the Legacy, Live Horizons/Beyond & Odyssey splits).
IME the worst people I have met in the game are insular BGS supporters of expansionist factions & their actions are mode agnostic. Fortunately by & large they are not in Legacy either